An unsafe level of a naturally occurring toxin was detected in algae blooms at Rufus Woods Lake near Bridgeport, the U.S. Army Corps of Engineers said Friday afternoon.

Officials posted Washington State Department of Health warnings against swimming, water skiing and other in-water activities at the lake near Bridgeport.

The toxin of concern is anatoxin-a, a nerve toxin produced by some blue-green algae blooms found in water bodies throughout the state. The toxin can be lethal to animals if ingested at high enough concentrations.

While it’s safe to eat properly cleaned and gutted fish, the water should not be consumed and steps should be taken to keep livestock and pets away from the water. Boaters are advised to avoid areas where algae blooms are present, officials advised.

Samples of floating algae blooms were taken and forwarded to King County Environmental Laboratories for testing and analysis. Test results indicate that samples contained up to 73 anatoxin-a micrograms per liter of water, which exceeds Department of Health recreational guidelines of one microgram per liter.

Tests also revealed presence of microcystin, a cyanobacterial toxin that primarily affects the liver in animals, but concentration levels were below Department of Health guidelines. A sample of lake water collected near the algae blooms did not contain any toxin.

The state departments of Ecology and Health notified the Corps that the analyzed samples are in excess of the state recommendation of one microgram per liter for recreational uses of the water. Samples will continue to be taken and analyzed weekly until anatoxin-a levels are determined to be below state recreational guidance values.